In general, gas turbines combust a mixture of compressed air and fuel to produce hot combustion gases. The combustion gases may flow through one or more turbine sections to generate power to drive a load, such as an electrical generator and/or a compressor. Within the gas turbine sections, the combustion gases typically flow through one or more stages of nozzles and blades (or buckets). The turbine nozzles may include circumferential rings of stationary vanes that direct the combustion gases to the rotating blades or buckets attached to the turbine rotor. The combustion gases drive the buckets to rotate the rotor, thereby driving the load. The hot combustion gases are contained using seals between circumferentially-adjacent arcuate segments of stationary shrouds surrounding the nozzle vanes and/or buckets; between the platforms of circumferentially-adjacent rotating buckets or bucket segments on a rotor wheel; and seals between axially adjacent nozzle and bucket shrouds of the same or successive turbine stages.
The seals are designed to prevent or minimize ingestion of higher-pressure compressor discharge or extraction flows into the lower-pressure hot gas path. Nevertheless, leakage about the seals is inevitable and results in reduced compressor performance which contributes to an overall reduction in the efficiency of the turbine.
At the same time, the hot gas path components, including the shroud segments, buckets and seals must be cooled to withstand the extremely high combustion gas temperatures. Conventional cooling schemes usually involve some combination of internal cooling features and associated cooling technique (for example, impingment, serpentine, pin-fin bank, near-wall cooling) where the cooling air is eventually exhausted through film-cooling holes that enable additional cooling of the surface of the component, or exhausted into the hot gas path. In some instances, however, it is not desirable to exhaust all or part of the internal cooling flow in this manner.
While various techniques have been employed to cool the shrouds, buckets and associated seals, it remains desirable to provide enhanced cooling for the shrouds, buckets and/or seals, and to use the heated or spent cooling air for at least one other purpose, for example, to further reduce the leakage of compressor air into the hot gas path.